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Intramolecular charge transfer dual fluorescent sensors from 4-(dialkylamino)benzanilides with metal binding site within electron acceptor

All Rights Reserved. Intramolecular charge transfer dual fluorescent sensors from 4-(dialkylamino)benzanilides with metal binding site within electron acceptor. Liu, Li-Hong; Zhang, Han; Li, Ai-Fang; Xie, Jian-Wei; Jiang, Yun-Bao ( Department of Chemistry, Key Laboratory of Analytical Sciences, Ministry of Education, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Peop. Rep. China). Tetrahedron, 62(44), 10441-10449 (English) 2006 Elsevier Ltd. CODEN: TETRAB.Chemical with cas number 858128-65-1 also plays role. ISSN: 0040-4020. DOCUMENT TYPE: Journal CA Section: 79 (Inorganic Analytical Chemistry) Three fluoroionophores (2a-c) were designed as the intramol. charge transfer (CT) dual fluorescent sensors for metal cations with metal binding site within the electron acceptor. These sensors were derived from 4-dialkylaminobenzanilides (alkyl = Me, Et, and n-butyl) with the amido Ph ring being an arm of 15-crown-5 thus bearing binding site for alk. and alk. earth metal cations. Compds. 2a-c were expected to have two possible CT channels of opposite direction. The absorption and fluorescence spectra of 2a-c and their crown-ether free model mols. 3a-c in a variety of solvents were recorded. Dual fluorescence was obsd. with 2a-c and was assigned to the LE and the CT states, resp. In nonpolar or less polar solvents the CT occurring with 2a-c was identified as that occurred with benzanilides (BA) with the amido anilines being the electron donor (the BA-like CT), while in polar solvents such as acetonitrile (ACN), the CT was still mainly the BA-like. In the presence of alkali and alk. earth metal cations in ACN, the CT dual fluorescence underwent substantial changes so as increased total quantum yield, red-shifted LE band and enhanced CT to LE intensity ratio. Binding of the metal cations at the 15-crown-5 moiety of 2a-c was shown to turn the CT direction that the dialkylamino group in the binding complexes being the electron donor while the benzo-15-crown-5 moiety now being within the electron acceptor. The occurrence of this CT enhances metal cation binding to 15-crown-5 ether in 2a-c, which was confirmed by the obsd. higher metal binding consts. Compds. 2a-c as the CT dual fluorescent sensors operate under the mechanism of the metal cation binding induced switching of the CT character from the BA-like to that occurred with 4-(dimethylamino)benzamides (the DMABA-like). Compds. 2a-c therefore represent successful examples for the CT dual fluorescent sensors for cations with the metal binding site within the electron acceptor and can be employed as sensitive ratiometric fluorescent sensors for metal cations of improved sensing performance. .